Hyperbranched polymers are classified as dendritic polymers together with dendrimers. While related-art polymers generally have a string form, these dendritic polymers have a highly branched structure. Accordingly, expectations lie in practical application utilizing various characteristics in a respect of having a specific structure, a respect of having a nanometer size, a respect of being capable of forming surfaces retaining many functional groups, a respect of being capable of having a low viscosity compared with linear polymers, a respect of exhibiting a behavior like fine particles with little entanglement of molecules, and a respect of being capable of becoming amorphous to control their solubility in a solvent.
Hyperbranched polymers contain a mixture of linear and completely branched repeating units. On the contrary, idealized dendrimers do not have any linear repeating units, but only contain completely branched repeating units.
An advantage of the hyperbranched polymer over the dendrimer is in its simplicity for synthesis, which is advantageous particularly in industrial production. Generally, while the dendrimer is synthesized by repeating protection and deprotection, the hyperbranched polymer is synthesized by a one-step polymerization of a so-called ABX type monomer having in one molecule thereof, three or more substituents of two types.
As a method for producing the hyperbranched polymer, the method by photopolymerization of a compound having a dithiocarbamate group with a photopolymerization initiating ability and having a styryl group and/or an acryl group has been known.
For example, a method for synthesizing a hyperbranched polymer by a photopolymerization of a styrene compound having a dithiocarbamate group (see Non-Patent Documents 1, 2 and 3), a method for synthesizing a hyperbranched polymer having a dithiocarbamate group by a photopolymerization of an acryl compound having a dithiocarbamate group (see Non-Patent Documents 4, 5 and 6) and a method for synthesizing a hyperbranched polymer having a dithiocarbamate group at a terminal of a molecule in which acid anhydrides are introduced in the main chain thereof by a photopolymerization of a styrene compound having a dithiocarbamate group and maleic anhydride that are coexisting (see Non-Patent Document 7) has been known.
In such a method for producing a hyperbranched polymer by a photopolymerization, expensive and special reaction facilities are required because a light source such as a high-pressure mercury lamp is used.
In addition, a problem of generating a large amount of a gelation product nearby a high-pressure mercury lamp occurs in such a photopolymerization. Therefore, only about 40% of the hyperbranched polymer can be obtained because the polymerization can be performed at a conversion ratio of only about 50% and purification by reprecipitation is repeated due to the large amount of remaining monomers. In addition, a cumbersome operation of removing a gelation product is also required.
Moreover, the photopolymerization also has a problem in which it is difficult to produce a hyperbranched polymer having the same molecular weight and the same degree of branching because the condition setting of the photoreaction is difficult when scaling up the reaction.
As described above, the method for producing a hyperbranched polymer by photopolymerization is difficult to perform in industry. Therefore, an excellent industrial production method has been desired.
Meanwhile, a method for polymerizing monomers having a styryl group and/or an acryl group by heating in the presence of a radical initiator such as a compound having a dithiocarbamate group and azobisisobutyronitrile (AIBN) has been known (see Patent Documents 1, 2, 3 and 4).
In this method, a linear polymer is obtained because the polymerization proceeds at a position of double bond of a styryl group and/or an acryl group.
In addition, an example of polymerization of 4-vinylbenzyl N,N-diethyldithiocarbamate that is a compound in which a dithiocarbamate group and a styryl group coexist in a molecule thereof by heating in the presence of AIBN, similar to the method as described above, has been known (see Non-Patent Document 8).
In this method, a linear polymer is obtained because the polymerization proceeds at a position of double bond of a styryl group.
In addition, Non-Patent Document 8 discloses an example of heating 4-vinylbenzyl N,N-diethyldithiocarbamate at 30° C. in the absence of AIBN. However, almost no reaction proceeds in this example (yield 0.8%).
As described above, there is no example of report in which a hyperbranched polymer is obtained by polymerizing a compound containing a dithiocarbamate group and a polymerizable unsaturated bond group such as a styryl group and/or an acryl group by heating.
Non-Patent Document 1
Koji Ishizu, Akihide Mori, Macromol. Rapid Commun. 21, 665-668 (2000)
Non-Patent Document 2
Koji Ishizu, Akihide Mori, Polymer International 50, 906-910 (2001)
Non-Patent Document 3
Koji Ishizu, Yoshihiro Ohta, Susumu Kawauchi, Macromolecules Vol. 35, No. 9, 3781-3784 (2002)
Non-Patent Document 4
Koji Ishizu, Takeshi Shibuya, Akihide Mori, Polymer International 51, 424-428 (2002)
Non-Patent Document 5
Koji Ishizu, Takeshi Shibuya, Susumu Kawauchi, Macromolecules Vol. 36, No. 10, 3505-3510 (2002)
Non-Patent Document 6
Koji Ishizu, Takeshi Shibuya, Jaebum Park, Satoshi Uchida, Polymer International 53, 259-265 (2004)
Non-Patent Document 7
Koji Ishizu, Akihide Mori, Takeshi Shibuya, Polymer Vol. 42, 7911-7914 (2001)
Non-Patent Document 8
Takayuki Otsu, Keiji Yamashita, Kazuichi Tsuda, Macromolecules Vol. 19, No. 2, 287-290 (1986)
Patent Document 1
Japanese Translation of PCT International Application No. 2002-508409
Patent Document 2
Japanese Translation of PCT International Application No. 2002-500251
Patent Document 3
Japanese Translation of PCT International Application No. 2004-509181
Patent Document 4
Japanese Patent Application Publication No. JP-A-5-188658